The present invention relates to a cutting blade, and more particularly to a cutting blade for use in cutting hard but brittle materials such as semiconductors (e.g., silicon and germanium), quartz, ferrite and glass.
A drastic development of the electronic industry in recent years has produced the need of miniaturized electronic devices or parts in large quantities. Generally, for the production of electronic parts, a large mass of the material is cut to pieces and then ground, lapped and further worked into minute parts. The cost for manufacturing electronic parts is greatly affected by the speed and accuracy with which the material is cut and by the amount of the material loss in cutting.
In the conventional cutting process, a large mass of material is trimmed into a suitable shape and then sliced with a thin cutting wheel having abrasive grains of diamond, cubic boron nitride (CBN) or the like affixed to its surfaces. Various cutting blades are used which include peripheral cutting edge blades, ID blades (inside diameter blades), reciprocating steel band blades and high-speed endless band saws. In view of the fact that the materials to be sliced for producing electronic parts are generally expensive and of high grade and have to be cut into very thin pieces, a cutting blade should be as thin as possible to minimize the cutting material loss and thereby reduce the manufacturing cost.
A peripheral cutting edge blade is a disk, to the outer periphery of which abrasive grains are secured. In cutting, the disk is rotated at a high speed. Although a thinner blade can be obtained by using a thinner disk, this will lower the rigidity of the blade and make the blade liable to deflect due to the resistance with which it meets during cutting operation. Deflection of the blade is a hindrance to an accurate cutting especially in case a large mass of material is to be cut.
An ID blade, which is most suitable for slicing, is a thin disk having a center hole. Grains of diamond, etc. are secured by electrodeposition to the inner edge of the center hole. The ID blade is strained for higher rigidity in the same manner as when a skin is stretched over either end of a drum. For cutting operation, the ID blade is subjected to a high-speed revolution.
Among the reciprocating steel band blades, there are two types, i.e., fixed grain type and loose grain type. In either of the blades, a thin steel band is stretched and subjected to reciprocating motion for cutting. A high-speed endless band saw includes a steel band having the ends joined together and is tightly stretched around two pulleys and rotated at a high speed. Grains of diamond are affixed to the underside of the steel band.
In order to obtain a thin blade, electrodeposition is a prevalent way of affixing abrasive grains to the surfaces of an ID blade, fixed grain type reciprocating band blade and high-speed endless band saw. This is because electrodeposition does not include any heating process such as sintering or brazing which can cause deflection of a thin base plate. Being typical of thin cutting blades for slicing and in general use for slicing a mass of silicon, an ID blade poses the following problems:
FIG. 1 is a sectional view of a conventional cutting blade to which abrasive grains are secured by electrodeposition. In case of an ID blade, a thin base plate 1 is made of stainless steel with a thickness of approximately 0.1 mm. Grains 2 of diamond, etc. are bonded to the base plate 1 through nickel bond 3 by electrodeposition. Since the grains 2 are bonded only in a single layer, the life of such a cutting blade runs out as soon as the grains 2 at the inner end get worn out or crush. Consequently cutting blades have to be replaced frequently for a given amount of work. As for the size of abrasive grains, it is evident that the coarser the grains are, the higher cutting speed can be obtained and the longer life the cutting blade has. On the other hand, the coarser the grains are, the larger the material loss is because the thickness of the cutting blade is the thickness of the base plate 1 plus twice the diameter of the abrasive grain 2. Also, the coarser the grains are, the more rugged the surface finish. In view of such factors, the conventional ID blades are normally provided with grains of diamond of 270 to 400 mesh, which are equivalent to 40 to 80 microns in diameter, and have a total blade thickness of 0.23 to 0.28 mm.
The second problem posed by the conventional ID blade is that because abrasive grains are bonded in a single layer to the inner edge of the center hole, the ID blade must be carefully centered when it is mounted on a slicing machine. Unlike metal- or resin-bonded wheels to which a thick layer of abrasive grains is bonded, the ID blade cannot be trued for accurate alignment once it has been mounted on a cutter. This alignment requires a great deal of skill and time.
In order to eliminate the above-described drawbacks, some of the ID blades have abrasive grains bonded in multilayers to the inner edges as shown in FIG. 2.
Even in this type of ID blades, however, abrasive grains are bonded in four or five layers at most. In addition, cutting blades having abrasive grains affixed by electrodeposition has an extremely higher density of abrasive grains than in metal- or resin-bonded blades. This poses a large disadvantage for blades having grades in multilayers. The cutting load applied on each abrasive grain is smaller so that the degree of what is called "the self-sharpening action", i.e., an action of keeping themselves sharp by being crushed in the course of cutting operation, will be less. In addition, because of small distances between the abrasive grains, the wear of the bond is less so that the abrasive grains will project less from the surface of the bond. This causes poor chip ejection and a short supply of cutting oil. Thus, the wheel is more likely to get loaded and requires frequent dressing to maintain the cutting accuracy. Therefore, it is difficult to adapt such an ID blade to an automatic cutting machine.